Bacteriophages have been isolated that infect some of the Bacteriodes fragilis subspecies as listed in the 8th edition of Bergeys Manual. The subspecies on which most of our phage have been isolated (35 isolates) include fragilis, thetaiotaomicron and "high theta" (these organisms are phenotypically similar to B. thetaiotaomicron but their DNA have a higher G plus C Mol% and there is little homology between the DNA of the two groups of organisms). Both lytic and temperate phage have been isolated. Research will include experiments on: the biology of the phage, transduction and characterization and nucleotide sequence similarities among phage nucleic acids. Additional phage will be isolated from the B. fragilis subspecies ovatus, vulgatus, and distasonis. The serological relationships of the phage are being determined by the method of inactivation rate constants. A phage typing system for the rapid identification of the clinically important subspecies fragilis is being developed. Temperate phages will be used to attempt transduction of those phenotypic characteristics that are variable among our bacterial cultures and also induced auxotropic and drug resistent mutations. The phage nucleic acids are being characterized (the nucleic acid in the phage that have been investigated is double stranded DNA) as to size and % G plus C. DNA homology between phage DNA preparations and between host and phage DNA preparations is being determined.